The invention is particularly concerned with methods of operating a controllable multi-variable process and systems for use in the operation of such a process. Methods and systems of this kind are described in GB-A-2 363 647 and GB-A-2 378 527 in which a multi-dimensional display representation of the variables is derived according to individual, parallel or other spaced coordinate axes. The variables of the process are of two kinds, namely, process-variables, of which the current values are generally available during process operation, and quality-variables, of which the values are generally determined later by laboratory or similar measurement or analysis. A boundary or envelope for prospective operation of the process is defined within the system of axes in accordance with sets of values for the process- and quality-variables accumulated respectively from previous multiple operations of the process. Each previous operation is defined as a respective datapoint consisting of a set of values for the individual process- and quality-variables applicable to that operation.
The multi-dimensional display representation of these earlier-described methods and systems is of advantage in the control of the process by identifying in relation to the defined envelope whether the current operating point as represented by the current values of the process-variables, lies within the range of past experience, and facilitates prediction of the likely outcome of the process. It is an object of the present invention to provide a method of operating a controllable multi-variable process, and a system for use in the operation of such a process, of improved form.